Resistance heated furnace



April 20, 1965 M. o. ROBINSON RESISTANCE HEATED FURNACE Filed Sept. 7, 1962 I N VEN TOR R06 /nson l Wm.

Me/l//n O.

BY l

United States Patent 3,179,735 RESSTANCE HEATED FURNACE Meivin 0. Robinson, Midland, Mich., assigner to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Sept. 7, 1962, Ser. No. 222,169 S Claims. (Cl. 13-20) The invention Vrelates to furnaces, particularly those furnaces which are suitable for graphitizing carbon articles. It more particularly concerns such a furnace having an improved electrical heating electrode assembly.

One of the objects of the invention is to provide an improved electrically heated graphitizing furnace in which objects to be graphitized become heated, gr-aphitized, and cooled in one continuous passage through the furnace.

Another object of this invention is to provide an irnproved electrode assembly for use in graphitizing furnaces which is capable of operation for extended periods of time without need for replacement.

A further object of this invention is to provide an improved electrode assembly for use in graphitizing furnaces which is capable of operation over an extended period of time and is easily replaced without dismantling the furnace in which it is installed.

In accordance with this invention, a graphitizing furnace, of the general type vdescribed and claimed in U.S. Patent No. 2,621,218, entitled Graphitizing Furnace, issued December 9, 1952, to Paul R. Juckniess, is provided with an improved elect-rode assembly in which a pair of resistance electrodes extend across the furnace in end to end abutting relationship, their abu-tting ends being heldy together in controlled pressure contact. The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

FIG. 1 is a transverse sectional View of a graphitizing furnace having incorporated therein an electrode -assembly in accordance with this invention, Iand FIG. 2 is a plan view of a pair of electrodes, as used in the furnace shown in FIG. 1, joined in end-to-end abutting relationship. p

Referring Vto FIG. 1there is shown, in transverse cross section, a grapbitizing furnace of the general type described yand claimed in the previously mentioned US. Patent No. 2,621,218 to Juckniess.

The furnace 10 includes foundation members 12, 18 and 14, 16 which support the outer wall parts 20, 22 and 24, 26, respectively, plus the inner wall parts 34, 36 and 42, 44, respectively. An outer wall top structure 28 extends between the outer wall members 24, 26 and is held in position by the members 30, 32.

An inner wall top structure composed of longitudinally extending planks'46, 48, 50, 52 and beams 54, 56, 58 extends 'between the inner side wall members 42, 44. The space between the inner and outer wall and top structures is, as shown, preferably filled with lamp black.

A pair of rails 60, 62 for supporting the slabs 61, 63 to be grap-hitized, the slabs 6-1, 63 being supported between the rails 66, 62 yand a pair of guide bars '72, 74.

The side wall members 42, 44, inner wml top structure and the members 3S, 40 define a heat generating chamber into which the electrode assembly of this invention eX- tends.

The heat generating chamber is normally not filled with lamp black. 'Lamp black 66, however, is `disposed between the rails 6i), 62 and -between those rails and the inner side wall structures 14, 16 and 34, 36 up to or near the level represented by thetop of the rails 60, 62.

The outer side wall members 20, 22 and the inner side wall members 42, 44 have slots 21, 23 and 76, 78, respectively, through which electrodes 80, 82 extend.

Each of the .electrodes is made of graphite and is rectangular in configuration when viewed in plan as in FIG. 2. While the electrodes 80, 82 lare of more or less uniform thickness, the end sections 84, 86 are tapered to a substantially reduced thickness at the en-d. i

The electrodes 80, 82 are inserted through the slots 21, 76 and 23, 78, respectively, and aligned with each other, their tapered end parts abutting, as at 88 and contacting the top o-f the member 38 which is part of the bottom of the heat generating chamber.

The brackets 102, 104, secured to the wall members 20, 22, respectively, extend outwardly beyond the ends of the electrodes S0, 82 but in axial alignment with the electrodes.y

Electrical leads 106, 108, including water cooling means, are coupled to the electrodes Si), S2 by means of lead ends 90, 92 which extend into the bores 94, 96, respectively (see FIG. 2), in the ends of the electrodes 80, 82. The ends 90, 92 are usually soldered to the walls ofthe bores 94, 96.

Means 9S, 10) of any suitable kind, such as a screw actuated device, are provided for maintaining the anodes 8), S2 forced against one another at the junction 88.

The leads 106, 168 are connected to a suitable electrical energization source, not shown.

In operation, the furnace 10 operates generally as does the furnace shown and claimed in U.S. Patent No. 2,621,- 218 to Juckniess except for the electrode assembly.

Although only one pair of electrodes has been illustrated in connection with this invention, it should be realized that several pairs of electrodes are usually incorporated in such furnaces.

Because the top of the member 38 is below the point where the electrodes 80, 82 pass through the furnace walls, the electrodes 80, 82 do not buckle when pressure is applied through the means 98, 10?.

As electrical current is passed through the electrodes the tapered ends are gradually consumed, but adjustment of the pressure on the electrodes may be made until the electrodes are forced against each other with sufficient force to provide and maintain a predetermined potential drop across the electrodes.

ln the operation of graphitizing furnaces made in accordance with the Iuckniess patent previously referred to, single electrodes having a thinned central section extended between the walls of the furnace. Such electrodes often break after only a few days (or even hours) of operation due to stresses existing in the heated furnaces. When such an electrode broke, it was necessary to remove the electrode and replace it. This meant dismantling part of the furnace, which is a time consuming as well as a costly operation.

The electrodes of this invention, being already in two parts and not being self-supporting from one side of the furnace to the other, provide an improved, longer lived anode assembly. Further, when the electrodes become consumed to the point where their replacement is indicated, the used electrodesfare withdrawn and new electrodes inserted, often without shutting down the furnace to replace individual pairs of electrodes.

In actual practice, electrodes in accordance with this invention usually `last several times as long as do the electrodes disclosed in the previously mentioned Juckniess patent. In one set of electrodes in accordance with this invention, the electrodes are l inch thick in the iin-tapered part, 8 inches -wide and 30 inches long. The last 12 inches of the electrode are tapered from 1 inch of thickness to 1A inch of thickness at the end.

What is claimed is:

1. In an electrically heated furnace having side walls en ab and a box-like heat generating compartment including a rectangular top, bottom, end walls, and side walls having means for passing electrodes therethrough, the heat generating compartment being disposed Within said furnace between said side walls, the side walls having means for passing electrodes therethrough, said means being disposed in predetermined relationship with respect to said means for passing electrodes through the side walls of the heat generating compartment, the improvement comprising a heating electrode assembly including at least one pair of planklike graphite electrodes having reduced thickness at one end, one of said electrodes extending through said side wall of the furnace and heat generating compartment from each side thereof, said electrodes being in end to end contact at their reduced thickness ends, said electrodes being disposed against the bottom of said heat generating compartment at their ends having reduced thickness, means for coupling an electrical lead to each of said electrodes, and means for urging said electrodes against one another under predetermined pressure.

2. A furnace in accordance with claim 1, wherein said bottom of the heat generating compartment is below the means for passing electrodes through the side walls of the furnace and the side walls of the heat generating compartment.

3. A furnace in accordance with claim l, wherein said means for urging said electrode against one another comprises screw means coupled to the side walls of said furnace.

4. A furnace in accordance with claim l, wherein a plurality of pairs of electrodes are disposed in side by side relationship within said heat generating compartment.

5. A furnace in accordance with claim 1, wherein said bottom of said heat generating compartment is made of graphite.

References Cited bythe Examiner UNITED STATES PATENTS 1,897,004 2/33 Heyroth 13-20 2,543,708 2/51 Rice et al. 13-20 X 2,621,218 12/52 Juclmiess 13-20 X 2,768,277 10/56 Buck et al. 13-20 X RTCHARD M. WOOD, Primary Examiner.

ANTHONY BARTlS, Examiner. 

1. IN AN ELECTRICALLY HEATED FURNACE HAVING SIDE WALLS AND A BOX-LIKE HEAT GENERATING COMPARTMENT INCLUDING A RECTANGULAR TOP, BOTTOM, END WALLS, AND SIDE WALLS HAVING MEANS FOR PASSING ELECTRODES THERETHROUGH, THE HEAT GENERATING COMPARTMENT BEING DISPOSED WITHIN SAID FURNACE BETWEEN SAID SIDE WALLS, THE SIDE WALLS HAVING MEANS FOR PASSING ELECTRODES THERETHROUGH, SAID MEANS BEING DISPOSED IN PREDETERMINED RELATIONSHIP WITH RESPECT TO SAID MEANS FOR PASSING ELECTRODES THROUGH THE SIDE WALLS OF THE HEAT GENERATING COMPARTMENT, THE IMPROVEMENT COMPRISING A HEATING ELECTRODE ASSEMBLY INCLUDING AT LEAST ONE PAIR OF PLANKLIKE GRAPHITE ELECTRODES HAVING REDUCED THICKNESS AT ONE END, ONE OF SAID ELECTRODES EXTENDING THROUGH SAID SIDE WALL OF THE FURNACE AND HEAT GENERATING COMPARTMENT FROM EACH SIDE THEREOF, SAID ELECTRODES BEING IN END TO END CONTACT AT THEIR REDUCED THICKNESS ENDS, SAID ELECTRODES BEING DISPOSED AGAINST THE BOTTOM OF SAID HEAT GENERATING COMPARTMENT AT THEIR ENDS HAVING REDUCED THICKNESS, MEANS FOR COUPLING AN ELECTRICAL LEAD TO EACH OF SAID ELECTRODES, AND MEANS FOR URGING SAID ELECTRODES AGAINST ONE ANOTHER UNDER PREDETERMINED PRESSURE. 